Jüttner, Ingrid; Chimonides, James; Cox, Eileen J.

Abstract

Species of the genus Achnanthidium including Achnanthidium pyrenaicum (Hustedt) Kobayasi and morphologically similar taxa are common and abundant in streams of the Himalaya in Nepal and north-west India. They were investigated with respect to their morphology and ecology, exploring their response to gradients in altitude, water chemistry, habitat characteristics, and their geographical distribution. One new species Achnanthidium rostropyrenaicum was described. Two species are closely related to taxa known from other locations in east and south-east Asia but were not formally described due to the small differences and the absence of molecular studies. The species investigated sometimes co-occur in the same streams and require careful taxonomic studies including the use of scanning electron microscopy to identify and separate them consistently. They differ with respect to their ecological niche, some respond more clearly to gradients in water chemistry while others respond to gradients in habitat characteristics. Similar studies on other taxonomic groups with several closely related but distinct taxa are needed so that diatoms can be used efficiently as indicators of environmental change in Himalayan freshwaters.